A pH Meter
is a device used for potentiometrically measuring the pH, which is
either the concentration or the activity of hydrogen ions, of an aqueous
solution. It usually has a glass electrode plus a calomel reference electrode,
or a combination electrode. pH meters
are usually used to measure the pH of liquids, though special probes are
sometimes used to measure the pH of semi-solid substances.
The concept of pH was defined in 1909 by S. P. L. Sørensen, and electrodes were used for pH measurement in the 1920s.
In October 1934 Arnold Orville Beckman registered the first patent for a complete chemical instrument for the measurement of pH, U.S. Patent No. 2,058,761, for his "acidimeter", later renamed the pH meter. Beckman developed the prototype as an assistant professor of chemistry at the California Institute of Technology, when asked to devise a quick and accurate method for measuring the acidity of lemon juice for the California Fruit Growers Exchange (Sunkist). On April 8, 1935, Beckman's renamed National Technical Laboratories focused on the making of scientific instruments, with the Arthur H. Thomas Company as a distributor for its pH meter. In its first full year of sales, 1936, the company sold 444 pH meters for $60,000 in sales. In years to come, it would bring in millions.
Uses
Knowledge of pH
to greater or lesser accuracy is useful or critical in a great many situations,
including of course chemical laboratory work. pH meters of various types and quality can be
used for soil measurements in agriculture; water quality for water supply
systems, swimming pools, etc.; brewing, industrially or domestically;
healthcare, to ensure that solutions are safe when applied to patients or
lethal as sterilants and disinfectants; and many other applications.
Circuit and Operation
Basic
potentiometric pH meters simply measure the voltage between two electrodes and
display the result converted into the corresponding pH value. They comprise a
simple electronic amplifier and a pair of probes, or a combination probe, and
some form of display calibrated in pH. The probe is the key part: it is a
rod-like structure usually made of glass, with a bulb containing the sensor at
the bottom. Frequent calibration with solutions of known pH, perhaps before
each use, ensures the best accuracy. To
measure the pH of a solution, the probe is dipped into it.
History
The concept of pH was defined in 1909 by S. P. L. Sørensen, and electrodes were used for pH measurement in the 1920s.
In October 1934 Arnold Orville Beckman registered the first patent for a complete chemical instrument for the measurement of pH, U.S. Patent No. 2,058,761, for his "acidimeter", later renamed the pH meter. Beckman developed the prototype as an assistant professor of chemistry at the California Institute of Technology, when asked to devise a quick and accurate method for measuring the acidity of lemon juice for the California Fruit Growers Exchange (Sunkist). On April 8, 1935, Beckman's renamed National Technical Laboratories focused on the making of scientific instruments, with the Arthur H. Thomas Company as a distributor for its pH meter. In its first full year of sales, 1936, the company sold 444 pH meters for $60,000 in sales. In years to come, it would bring in millions.
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